Structural behaviour of an innovative precast cold-formed steel ferrocement as composite beam

Abstract

This research investigates the structural behaviour of simply supported composite beams, in which a ferrocement slab is connected together with cold-formed steel (CFS) beam by means of shear connectors. This system, called Precast Cold- Formed Steel-Ferrocement Composite Beam System, is designed to utilise the composite action between the CFS sections and ferrocement slab where shear forces are effectively transmitted between the beam and slab via shear connectors.CFS sections have been recognized as an important structural element in developed countries, and sustainable construction material for low rise residential and commercial buildings. However, it still is remains as insufficient data and information on the behaviour and performance of CFS as the composite construction in composite action is yet to be established. One limiting feature of CFS is the thickness of this section that makes it susceptible to torsional, distortional, lateral torsional, lateral distortional and local buckling. Hence, a reasonable solution is resorting composite construction of structural CFS section integrated with reinforced concrete deck slab. An efficient and innovative beam system of built-up CFS sections acting compositely with a concrete deck slab has been developed to provide an alternative composite system for floors and roofs in buildings. In this study, ferrocement is an alternative solution as concrete deck of a slab. It is a form of thin reinforced concrete structure, in which a strong cement-sand mortar matrix is reinforced with closely spaced, multiple layers of thin wire mesh or small diameter rods, uniformly dispersed throughout the matrix of the composite. This study mainly comprises three major components; experimental work, theoretical analysis and finite element analysis using ANSYS (version 11). Experimental works involved small-scale and full-scale testing of laboratory tests. The first phase of test program comprised often push-out test specimens and eighteen full-scale CFS-ferrocement composite beam specimens. Push-out tests were carried out to determine the strength and behaviour of the shear transfer enhancement between the CFS and ferrocement.Three types of shear connectors (bolts, self-drilling screws, bar angle) were tested and 2, 4 and 6 layers of wire mesh in ferrocement cold formed were proposed. The expression for predicting the capacity of shear connector in which bolt with 12mm diameter is best to be considered to transfer shear force into steel section-ferrocement slab interface. The second phase of test program comprised of a total of eighteen full-scale simply supported composite beams with variable parameters and tested to failure. The main variables considered in the study are the shape of section (I- and C-section as beam), thickness (2mm, 3mm and 4mm) of the CFS section and number of wire mesh layer (2, 4 and 6 layers). Four points load bending system was used to test the specimens. The plastic analysis results depicted that the ultimate bending capacity of a ferrocement CFS composite beam can be estimated by using conventional equilibrium procedures and the constitutive laws prescribed by Euro codes. The finite element and theoretical model showed agreement with the experimental results based on the moment versus deflection curves of the proposed composite beam system.